1. Field of the Invention
The present invention relates to a digital image sensing apparatus and, more particularly, to a digital image sensing apparatus that quickly generates a high-quality image with a smaller number of pixels than that of an image sensing device mounted in the image sensing apparatus.
2. Description of the Related Art
Along with the recent rapid spread of personal computers, the demand for digital cameras serving as image input devices is increasing. In addition, high-quality recording apparatuses such as digital video recorders are widely used as moving image recorders.
The image quality of an electronic still camera depends on several factors. Especially, the number of pixels of an image sensing element is a very important factor for the resolution of a sensed image. Some recent commercially available electronic still cameras have more than 5 million pixels. However, data of 5 million pixels is not always necessary for all application purposes. Images displayed on the Webs of the Internet often have, if anything, smaller pixel sizes.
In current digital cameras, the transfer time from the image sensing element to the image memory is a bottleneck. Most models having a large number of pixels cannot execute high-speed continuous shooting. In addition, even digital cameras need to have a moving image sensing function as an additional function. Hence, transfer to the memory must be done at a high speed. For this purpose, the data amount to be processed is preferably reduced in advance.
When the number of pixels of an output image is smaller than that of the image sensing element, the number of pixels to be used is limited in advance. Alternatively, a plurality of pixels are averaged and read out by one clock. With this processing, the amount of data to be transferred from the image sensing element to the memory can be reduced, and the memory transfer rate can be increased.
In size reduction by linear interpolation, an image having a large size is generated by using all pixels. Then, an image with a small size is generated by linear interpolation.
Such resizing by linear interpolation can ensure a high image quality. However, since linear interpolation is executed by using all pixel data, the arithmetic amount is large. Hence, this method is inappropriate for the above-described continuous shooting function or moving image sensing.
There is a method of reducing the data amount of memory readout, in which an integration function is added to the image sensing element so that a reduced image is generated by reading out a small number of averaged data. Jpn. Pat. Appln. KOKAI Publication No. 2001-245141 discloses a high-speed image reducing method using this method.
Jpn. Pat. Appln. KOKAI Publication No. 2001-016441 discloses an apparatus that executes data thinning and also corrects distortion of data when the number of resolutions is limited. An embodiment of this reference discloses creation of 400-dpi data by an apparatus having a resolution of 600 dpi. When 600-dpi data is directly thinned out, the data is distorted. To cope with this, pixel data to compensate for the distortion of positions is generated from the 600-dpi data by linear interpolation. The apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-016441 creates 400-dpi data by executing interpolation totally using all 600-dpi data obtained by scanning.